Engines, including diesel engines, gasoline engines, and natural gas engines, for example, may exhaust a complex mixture of emissions to the environment. The emissions may include both gaseous compounds and solid material. The solid material in exhaust emissions may include, for example, particulate matter. Particulate matter may include ash and unburned carbon particles generally referred to as soot.
Environmental concerns have resulted in the development of systems to treat engine exhaust in a variety of ways. Some of these systems may employ exhaust aftertreatment devices, such as particulate filters, to remove particulate matter from the flow of engine exhaust. A particulate filter may include a filter substrate material designed to capture the particulate matter. After a period of engine operation and use of the particulate filter, the filter substrate material may become partially saturated with the particulate matter being filtered out of the exhaust. This partial saturation may hinder the ability of the particulate filter to remove additional particulate matter from the exhaust flow, and also may adversely affect engine operation.
The collected particulate matter may be removed from the filter material through a process called regeneration in order to enable the filter material to continue its intended function of capturing particulate matter. A particulate filter may be regenerated by increasing the temperature of the filter material above the combustion temperature of the captured particulate matter. The increase in temperature to support oxidation of particulate matter may be effectuated by a regeneration assembly of the type that includes a combustion chamber. The combustion chamber may require an air supply system to support combustion. During regeneration, air may flow, via the air supply system, and mix with fuel to support combustion within the regeneration assembly and create enough heat to oxidize the particulate matter and regenerate the particulate filter.
It is sometimes the case that combustion air for a regeneration assembly is drawn from a boosted intake air supply for the engine. Regeneration may occur at preprogrammed times, or at times when a threshold accumulation of particulate matter in the particulate filter is detected. Such times may occur during machine operation when the engine is operating at various speeds and/or under various loads. Accordingly, the air supply, for example the air supply drawn from a boosted intake air supply for the engine, may vary. Accommodating a varying air supply while assuring reliable regeneration is sometimes accomplished with a somewhat sophisticated, i.e., “smart,” hydraulically actuated air valve capable of maintaining a constant air flow while depending on the varying air supply. It would be beneficial and desirable to be able to supply air to a regeneration assembly and achieve reliable regeneration with less sophisticated, and therefore less costly, air valves.
One system for supplying combustion air to a regeneration assembly is disclosed in U.S. Pat. No. 4,589,254, issued to Kume et al. on May 20, 1986 (“the '254 patent”). The '254 patent discloses a filter for exhaust gases, and a burner that may regenerate the filter. In the '254 patent, primary air is directed via one flow path to the burner at high pressure to atomize injected fuel, and secondary air is directed via another flow path to the burner at low pressure to support combustion during regeneration. A pressure regulating valve adjusts the flow rate of the primary air, and a flow control valve adjusts the cross-sectional area of the flow path for the secondary air. The system of the '254 patent includes a relatively complex arrangement including an array of diaphragm valves intended to control secondary air flow with high precision, regardless of variations in operation of an air pump, or fluctuations in atmospheric temperature or pressure in the secondary air line.
While the system of the '254 patent contemplates controlling air flow to a regeneration assembly, the system may be unduly complicated. For example, in the system of the '254 patent, various embodiments are disclosed requiring an arrangement including a pump, multiple diaphragm valves, and various connecting passageways for controlling the secondary combustion air. In addition, a separate pump, pressure regulating valve, and passageway are required to control the flow of primary air for atomizing fuel for combustion. Further, the system of the '254 patent fails to make provision for a low flow of air until ignition, and this failure may result in a further failure to generate a sustainable flame in the burner. Moreover, the system of the '254 patent may be overly complex, difficult to maintain in proper working order, and too expensive.
The disclosed air supply system for a regeneration assembly is directed toward improvements in the existing technology.